CHIMERIC IMMUNOGLOBULIN LIGHT-CHAINS ARE SECRETED AT DIFFERENT LEVELS- INFLUENCE OF FRAMEWORK-1 AMINO-ACIDS

Immunoglobulin light chain proteins are generally thought to be readil y secreted without their corresponding heavy chains; non-secreted ligh t chains have been viewed as aberrant forms. We have re-examined this assumption by expressing chimeric mouse-human light chains constructed for 12 mouse antibodies (mouse variable regions fused to a human kapp a light chain constant region) in Sp2/0 and CHO cells. Five of the 12 light chains were either poorly secreted or not secreted at all. There was approximately a five-fold difference in the levels of secreted li ght chain between the highest poor secretor and the lowest good secret or. All of these light chains formed functional chimeric IgGs, which w ere secreted at similar levels, when co-expressed with their respectiv e chimeric mouse-human heavy chains (mouse variable regions fused to a human gamma-1 heavy chain constant region). The influence of variable region amino acids on light chain secretion was examined by replacing the Framework-1 region of three poorly-secreted chimeric light chains with that of a readily-secreted light chain. For two of the light cha ins, secretion levels increased approximately 30- and 100-fold relativ e to that of the unmodified light chains. Comparison of the Framework- 1 amino acid sequence of the poorly- and readily-secreted light chains revealed an asparagine (N) and proline (P) at positions 11 and 12, re spectively of these poorly-secreted light chains and a leucine (L) and serine (S) in the same region for some of the readily secreted light chains. Alteration of the NP to LS for one of the poorly-secreted ligh t chains resulted in an approximately seven-fold increase in light cha in secretion over that of the native form of the poorly-secreted light chain. We conclude from these studies that poor secretion can be a na turally occurring state for normal light chains and that amino acids w ithin Framework-1 contribute to poor secretion for some of the light c hains.